Questions about a mach 2 attempt.

[pendrin2020]

So airfest is coming.

I'm already attempting my L3 that weekend, but I kinda want to try something gutsy. I see wildman's got these Mach 2 kits for $90 and I'd like to put one together in time for the event, but I've never flown that fast. So here's a few questions:

Are rail buttons a bad idea if you're going that fast?

I understand that aerodynamics change drastically above mach, is there a baro-based altimeter I can trust for accurate top speed data? If not, anyone know where in the hell I can find a Raven?

What are the big mistakes that every newbie to extreme performance make?

 

[Eric]

Type "Airfest" in the comments and get it for $69.

I dont think rail buttons will effect speed nearly as much as your build weight. I believe it will effect altitude more. Wildman also sell a printed airfoiled rail guide that worked well for me.

Or go with fly away rail guides.

 

[tim cubbedge]

As far as baro-based altimeter velocity, speeds at mach tend to get a little funky. Better off with an accelerometer based altimeter.

 

[pendrin2020]

That’s kinda what I’m thinking, but other than the raven, what is there?

 

[djs]

Altus Metrum, and Marsa. Lots of $$ tho!

 

[pendrin2020]

Exactly!

 

[pendrin2020]

What if I used baro or timers for recovery and use an Arduino with an accelerometer for data logging?

 

[Charles_McG]

The baro-alt will be flaky through Mach, but you could look at the alt v time curve before and after and get an idea of how fast it had to go in between. Would that be good enough?

 

[mpitfield]

My baro is close enough over Mach 2 and matches my sims and accelerometer, well close enough. Baro is mostly funky going through Mach but a lot of the noise goes away once you get through it. Using a baro and accelerometer based altimeter would be ideal, but if budget is a concern I would put your money into a tracker. When it comes to the rail buttons I would use a FARG instead.

 

[pendrin2020]

FARG?

Edit: oh crap. Fall away rail guide. Duh

 

[dr wogz]

What's the saying..

Speed, is only a question of money. How fast you wanna go depend on how much you got!

 

[tim cubbedge]

FARG?

Edit: oh crap. Fall away rail guide. Duh

Close, Fly Away Rail Guide.

 

[mpitfield]

FARG?

Edit: oh crap. Fall away rail guide. Duh

Yeah sorry I am in IT and we love our TLAs or in this case FLAs

 

[pendrin2020]

I’m a programmer... I get it, bro! Lol

 

[cwbullet]

He just had a 69$ deal on the kit. Could not let it pass.

 

[boatgeek]

It wasn't quite Mach 2, but the high school club I work with flew to M1.6 on two baro-based altimeters: a Stratologger CF and an Eggtimer Quark. As long as they have Mach lockouts/Mach immunity listed in the features you should be OK with a baro at M2. How high are you going?

 

[pendrin2020]

It wasn't quite Mach 2, but the high school club I work with flew to M1.6 on two baro-based altimeters: a Stratologger CF and an Eggtimer Quark. As long as they have Mach lockouts/Mach immunity listed in the features you should be OK with a baro at M2. How high are you going?

Not sure, still pondering whether or not to commit to the project.

 

[pendrin2020]

He just had a 69$ deal on the kit. Could not let it pass.

How do I get that discount? I’m in checkout and I’m not seeing it.

 

[tim cubbedge]

How do I get that discount? I’m in checkout and I’m not seeing it.

Look here!
https://www.rocketryforum.com/threads/airfest-altitude-contest.147088/

 

[pendrin2020]

Got it! Thanks!

 

[MikeyDSlagle]

For recording only, the Jolly Logic Altimeter 3 has an accelerometer...doesn't it? Would that do the trick?

 

[pendrin2020]

Actually, yeah that would be phenomenal.

 

[MikeyDSlagle]

It's a great little gadget to have. Works very well if you remember to use and and even more so when you turn it on.

 

[OverTheTop]

Have flown a Ravens to Mach 1.8 no problems.

One thing I would suggest is gluing the supercap to the PCB (as recommended in the manual). The high accels you will be experiencing during a speed run will rip it off the board otherwise. I use Loctite 401 CA adhesive.

Similarly, if you have a gps just run a thin layer of epoxy around the antenne where it is stuck (by double-sided tape) onto the PCB.

 

[Charles_McG]

Is it known which, if any, altimeters integrate acceleration to get altitude? That would be a double integral with noise to boot.

 

[markkoelsch]

Is it known which, if any, altimeters integrate acceleration to get altitude? That would be a double integral with noise to boot.

And would actually calculate distance travelled instead of altitude. Apogee is usually better determined by barometric and velocity is better determined by accelerometer.